Electric resistance alloy



Dec. 7, 1954 s POCH ELECTRIC RESISTANCE ALLOY Filed July .'51, 1951 FIG. 2

PEECENT COBALT xNvENToR Stephen Pac/7 ATTORN Ys United States Patent O ELECTRIC RESISTANCE ALLOY Stephen Poeh, Wyckoff, N. J., assignor to Driver-Harris Company, Harrison, N. J., a corporation of New Jersey Application July 31, 1951, Serial No. 239,543

4 Claims. (Cl. 201-63) This invention relates to electrical resistance elements, more particularly to an electrical resistance element having a low temperature coefficient of resistance and to methods of producing said elements.

Alloys of copper and nickel have heretofore been used to a great extent in the production of electrical resistance elements. Employing proportions of about 55% of copper and 45% of nickel, these alloys produce electrical resistance elements varying in resistivity from 240 to 290 ohms per circular mil foot. Variations in the value of the resistivity are due, in part, to the copper and nickel content of the alloy and also in part to minor constituents which are present in the alloy, either from their presence in the raw material from which the alloy is produced, or which enter as impurities during the melting process.

The impurities and amounts of impurities present in such alloys also have a direct relation to the temperature coeicient of electrical resistance. Due to the precision required in electronic equipment at the present time, it is desirable to provide electrical resistance elements having a temperature coeicient of resistance of zero, or substantially zero, so that the change in electrical resistance is less than a few parts per million over the range of temperature in which the alloy is to be used. An object of the present invention is to provide alloys of definite composition and with a temperature coefficient of resistance of substantially zero over a range of from to 100 C.

l have found that additions of cobalt to copper-nickel alloys of the approximate composition of 55 parts copper to 45 parts nickel, when the cobalt replaces an equivalent amount of nickel, can be employed to control the temperature coefficient of resistance as desired. A copper-nickel alloy free of cobalt has a negative coeicient of electrical resistance over this range, that is, its resistivity diminishes with increase in temperature. By adding cobalt in controlled amounts to an alloy of this composition, the change in resistance with temperature can be reduced to practically a zero value. If the additions are too great, a positive coeicient of resistance is obtained.

In some instances it may be desirable to produce alloys which will have definite negative coethcients or denite positive coetlicients and it is apparent that this may be accomplished by controlled additions of cobalt to an alloy of copper and nickel of the proportions herein stated.

In the accompanying drawings I have illustrated the use of the resistance element in a conventional resistor andJ have shown a chart of the effect of cobalt additions on the temperature coefficient of resistance of such an alloy. In this showing:

Fig. l is a front elevation of a conventional wire wound resistor, which is one type of apparatus in which electrical resistance elements are employed; and

Fig. 2 is a chart in which the temperature coeicient (20 to 100 C.) is charted against percentage of cobalt in an alloy of substantially 55 parts copper and 45 parts nickel.

Referring to Fig. 1 of the drawings, the resistor wire 1 is shown as wound upon a ceramic base 2. The electrical resistance element of the invention may, of course, be used in a number of devices other than a resistor of the type herein illustrated.

In a series of tests in which varied amounts of cobalt were added to a copper-nickel alloy of substantially 55 A parts copper and-45 parts of nickel, the

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following values were obtained:

Co Percent These values are plotted in Fig. 2 and a curve obtained which is substantially a straight line. In this chart, the percent of cobalt is plotted against the temperature coetiicient of resistance. Thus, the point 3 indicates the heat in which the amount of cobalt is 1.07% and in which the value of the temperature coetiicient of resistance is 0.000058. Likewise, the points 4, 5, 6, 7 and 8 represent the other tive alloys included in the preceding table. It will be noted that the alloy, with a cobalt content of 2.04%, produced an alloy having a temperature coecient of resistance equal to zero.

In the heats covered by the above table and the chart, Fig. 2, the copper content varied from 53.72% to 54.50%. Some of the heats were analyzed for carbon and had a carbon content of 0.01%. The balance of the alloy was cobalt, in the percentage stated, and nickel.

While other elements may be added to copper-nickel alloys to control the temperature coeicient of resistance, I have found that the regulated addition of cobalt not only permits the obtaining of an alloy having a zero temperature coetcient of resistance, but it also produces an alloy that is free from gas evolution when the wire to be used as an electrical resistance element is embedded in enamel, vitreous or non-vitreous, as is common in the commercial production of such devices. With the additions of other elements, such as iron, manganese or silicon, which may be used to regulate the temperature coeicient of resistance, evolution of gas by contact with the enamel occurs in the manufacturing process. Such alloys are, therefore, unsuitable whereas the cobalt containing alloy is suitable for the manufacture of electrical resistance elements of high precision.

As stated, the alloy preferably consists of about 55 percent copper and 45 percent nickel. The alloy has a low carbon content, less than 0.03 percent and preferably about 0.01 percent. The cobalt added is subtracted from the nickel content. The alloy may contain from 50 to 60 percent copper, from 1% to 21/2 percent cobalt and balance nickel.

I claim:

l. A wire Wound resistor comprising a ceramic base and a resistance wire on the base consisting essentially of 50 to 60 percent copper, 1.5 to 2.5 percent cobalt, balance nickel, and having a temperature coeiicient of electrical resistance between -4X10r5 and -}-3 10-5 over the range of temperature of 20 to 100 C.

2. A wire wound resistor comprising a ceramic base and a resistance wire on the base consisting essentially of substantially 55 percent copper, substantially 43 percent nickel, substantially 2 percent cobalt, and having a temperature coefficient of electrical resistance of substantially zero over the range of temperature of 20 to C.

3. An alloy consisting essentially of 50 to 60 percent copper, 1.5 to 2.5 percent cobalt, balance nickel, and having a temperature coettlcient of electrical resistance between -4 10*5 and -}-3 105 over the range of temperature of 20 to 100 C.

4. An alloy consisting essentially of substantially 55 percent copper, substantially 43 percent nickel, substantially 2 percent cobalt, and having a temperature coefticient of electrical resistance of substantially zero over the range of temperature of 20 to 100 C.

(References on following page) Y t s References Cited in the le of this patent OTHER REFERENCES UNITED STATES PATENTS 1Zeit(s)chrift fr Metallkunde, vol. 30, 1938, pages Number Name D 2,019,457 Lodge Oct. 29, 1-.935 5 

1. A WIRE WOUND RESISTOR COMPRISING A CERAMIC BASE AND A RESISTANCE WIRE ON THE BASE CONSISTING ESSENTIALLY OF 50 TO 60 PERCENT COPPER, 1.5 TO 2.5 PERCENT COBALT, BALANCE NICKEL, AND HAVING A TEMPERATURE COEFFICIENT OF ELECTRICAL RESISTANCE BETWEEN -4X10-5 AND +3X10-5 OVER THE RANGE OF TEMPERATURE OF 20* TO 100* C. 